Method of constant RPM control for a ventilation system

ABSTRACT

A method of constant airflow control includes various controls to accomplish a substantially constant airflow rate over a significant change of the static pressure in a ventilation duct. One control is a constant I·RPM control, which is primarily used in a low static pressure range. Another control is a constant RPM control, which is primarily used in a high static pressure range. These controls requires neither a static pressure sensor nor an airflow rate sensor to accomplish substantially constant airflow rate while static pressure changes.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to the concurrently filed applicationslisted below, the contents of which are incorporated herein by referencein their entirety.

Application Filing Attorney No. Date Title Docket No. 12/016,924 Jan.18, 2008 METHOD OF CONSTANT SNTEC.001AUS AIRFLOW CONTROL FOR AVENTILATION SYSTEM 12/016,894 Jan. 18, 2008 METHOD OF TRANSITIONSNTEC.001AUS3 BETWEEN CONTROLS FOR A VENTILATION SYSTEM 12/016,872 Jan.18, 2008 MULTI-LEVEL PROGRAMMING SNTEC.001AUS4 OF MOTOR FOR AVENTILATION SYSTEM 12/016,878 Jan. 18, 2008 COMPENSATION OF MOTORSNTEC.001AUS5 CONTROL USING CURRENT-RPM RELATION FOR A VENTILATIONSYSTEM 12/016,850 Jan. 18, 2008 MOTOR CONTROL APPARATUS SNTEC.001AUS6FOR A VENTILATION SYSTEM

BACKGROUND

The present disclosure relates to airflow control, and moreparticularly, to control of an electric motor for a substantiallyconstant airflow.

Discussion of Related Technology

A typical ventilation system includes a fan blowing air and aventilation duct to guide the air from the fan to a room or space to aircondition. An electric motor is coupled to the fan and rotates the fan.Certain ventilation systems also include a controller or control circuitfor controlling operation of the electric motor for adjusting therotational speed of the motor. The controller may change the electriccurrent supplied to the electric motor to adjust the rotational speed.In certain ventilation systems, the controller controls the operation ofthe motor to adjust the air flow rate, which is the volume of the airflowing through the duct for a given time period.

SUMMARY

One aspect of the invention provides a method of operating an electricmotor in a ventilation system. The method may comprise: detecting anelectric current applied to a motor; detecting a rotational speed of themotor; and controlling the motor's operation to adjust a product of theelectric current and the rotational speed so as to arrive a targetvalue.

In the foregoing method, the motor is coupled with a fan, which blowsair in a ventilation duct, wherein controlling the motor's operation maygenerate an airflow with a substantially constant airflow rate in theventilation duct in a range of a static pressure within the duct. Thesystem may not comprise an airflow rate sensor for detecting an airflowrate generated by the blower, wherein controlling the motor's operationdoes not use an input of an airflow rate change. Controlling the motor'soperation may generate the substantially constant airflow rate while thestatic pressure significantly changes. The system may not comprise astatic pressure sensor for detecting the static pressure within theduct, wherein controlling the motor's operation does not use an input ofa static pressure change.

Still in the foregoing method, controlling the motor's operation maycomprise adjusting a turn-on period of the motor so as to attempt tomake the product reach the target value. The target value may becomputed using a rated electric current and a rated rotational speed ofthe motor. The target value may be a fractional value of a product of arated electric current and a rated rotational speed of the motor. Themethod may further comprise: receiving a user input of a desired levelof airflow rate; and obtaining the target value that corresponds to thedesired level. Receiving the user input may comprise receiving a user'sselection among a plurality of predetermined levels, and whereinobtaining the target value may comprise retrieving the target value froma plurality of values stored in a memory, wherein the retrieved targetvalue may be associated with the user's selection. Receiving the userinput may comprise receiving a user's desired level represented in anumber, and wherein obtaining the target value may comprise computingthe target value using the number and a preprogrammed formula.

Still in the foregoing method, controlling the motor's operation maycomprise transitioning from adjusting the product to adjusting arotational speed of the motor to arrive another target value.Controlling the motor's operation may comprise transitioning toadjusting the product from adjusting a rotational speed of the motor toarrive another target value. The method may further comprise:determining whether the electric current is greater or smaller than areference value; and when the electric current is greater than thereference value, continuing to control the motor's operation so as toadjusting the product. The method may further comprise: determiningwhether the electric current is greater or smaller than a referencevalue; and when the electric current becomes smaller than the referencevalue, controlling the motor's operation so as to transition fromadjusting the product to adjusting a rotational speed of the motor toarrive another target value.

Another aspect of the invention provides a method of operating anelectric motor in a ventilation system. The method comprises: providinga blower comprising a motor and a fan coupled to the motor, the blowerbeing configured to generate an airflow in a ventilation duct; detectingan electric current applied to the motor; detecting a rotational speedof the motor; and controlling the motor's operation so as to generatethe airflow with a substantially constant airflow while a staticpressure within the duct substantially changes, wherein controlling themotor's operation does not use an input of a static pressure within theduct.

In the foregoing method, the system may not comprise a static pressuresensor for detecting a static pressure within the duct. The system maynot comprise an airflow rate sensor for detecting an airflow rategenerated by the blower, wherein controlling the motor's operation doesnot use an input of an airflow rate generated by the blower. Controllingthe motor's operation may comprise conducting a feedback control of aproduct of the electric current and the rotational speed so as to makethe product reach a target value. Controlling the motor's operation maycomprise conducting a feedback control of the rotational speed so as tomake the rotational speed reach a target value. Controlling the motor'soperation may comprise conducting a feedback control of a product of theelectric current and the rotational speed so as to make the productreach a target value.

The method may further comprise determining whether the electric currentis greater or smaller than a reference value, wherein the feedbackcontrol of the product is performed when the electric current is greaterthan the reference value. Controlling the motor's operation may comprisea feedback control of the rotational speed so as to make the rotationalspeed reach a target value. The method may further comprise determiningwhether the electric current is greater or smaller than a referencevalue, wherein the feedback control of the rotational speed is performedwhen the electric current is smaller than the reference value.

Another aspect of the invention provides a method of operating anelectric motor in a ventilation system. The method comprises: providinga blower comprising a motor and a fan coupled to the motor, the blowerbeing configured to generate an airflow in a ventilation duct;monitoring a rotational speed of the motor; monitoring an electriccurrent applied to a motor; and controlling the motor's operation so asto maintain the rotational speed within proximity of a target rotationalspeed while the electric current is smaller than a reference value.

In the foregoing method, controlling the motor's operation may generatea substantially constant airflow rate while a static pressure within theduct significantly changes. The system may not comprise an airflow ratesensor for detecting an airflow rate generated by the blower, whereincontrolling the motor's operation does not use an input of an airflowrate generated by the blower. The system may not comprise a staticpressure sensor for detecting the static pressure within the duct,wherein controlling the motor's operation does not use an input of astatic pressure within the duct. Controlling the motor's operation maycomprise adjusting a turn-on period of the motor so as to attempt tomake the product reach the target rotational speed. The method mayfurther comprise receiving a user's input of a desired rotational speed,which becomes the target rotational speed. The target rotational speedmay be a fractional value of a rated rotational speed of the motor.

The foregoing method may further comprise: receiving a user input of adesired level of the rotational speed, wherein the user input maycomprise a selection among a plurality of predetermined levels; andretrieving, from a memory, the target rotational speed associated withthe user's selection. The method may further comprise: receiving a userinput of a desired level of the rotational speed, wherein the userinputs the desired level represented in a number; and computing thetarget rotational speed using the number and a preprogrammed formula.The target rotational speed may be computed using the number and a ratedrotational speed of the motor. Controlling the motor's operation maycomprise transitioning from maintaining the rotational speed tomaintaining a product of the electric current and the rotational speedwithin proximity of another target value. The other target value may becomputed using a rated electric current and a rated rotational speed ofthe motor. Transitioning may occur when the electric current becomesgreater than the reference value.

Another aspect of the invention provides a method of operating anelectric motor in a ventilation system. The method comprising: providinga blower comprising a motor and a fan coupled to the motor, the blowerbeing configured to generate an airflow in a ventilation duct; detectingan electric current applied to the motor; detecting a rotational speedof the motor; and controlling the motor's operation so as to generatethe airflow with a substantially constant airflow while a staticpressure within the duct substantially changes, wherein controlling themotor's operation does not use an input of an airflow rate generated bythe blower.

The system may not comprise an airflow rate sensor for detecting changesof the airflow rate. The system may not comprise a static pressuresensor for detecting a static pressure within the duct, and whereincontrolling the motor's operation does not use an input of a staticpressure within the duct. Controlling the motor's operation may comprisea feedback control of the rotational speed so as to make the rotationalspeed reach a target value. Controlling the motor's operation maycomprise a feedback control of a product of the electric current and therotational speed so as to make the product reach a target value. Themethod may further comprise determining whether the electric current isgreater or smaller than a reference value, wherein the feedback controlof the product is performed when the electric current is greater thanthe reference value. Controlling the motor's operation may comprise afeedback control of the rotational speed so as to make the rotationalspeed reach a target value. The method may further comprise determiningwhether the electric current is greater or smaller than a referencevalue, wherein the feedback control of the rotational speed is performedwhen the electric current is smaller than the reference value.

Another aspect of the invention provides a method of operating anelectric motor in a ventilation system. The method comprising: running amotor in a first control mode, which attempts to make a I·RPM valuereach a first target value, wherein the I·RPM value is a product of anelectric current and the rotational speed of the motor; running themotor in a second control mode, which attempts to make the rotationalspeed reach a second target value; and transitioning between the firstcontrol mode and the second control mode.

The foregoing method may further comprise: comparing the electriccurrent with a reference value; and wherein transitioning may be carriedout based on a result of the comparison. Comparing may be continuously,periodically or sporadically performed during running of the motor. Thereference value may be a user's input or a value computed using a user'sinput for at least one of the first and second control modes. The methodmay further comprise receiving a user input of a desired level ofairflow. The desired level may be a fractional value of a maximumairflow rate, and wherein the reference value may be computed using thefractional value. The reference value may be a product of the fractionalvalue and a rated electric current of the motor. The first target valuemay not change while running in the first control mode, and wherein thesecond target value may not change while running in the second controlmode. The first control mode may be chosen when the electric current isgreater than the reference value. The second control mode may be chosenwhen the electric current is smaller than the reference value. The motormay run in the first control mode at a first static pressure within aventilation duct, wherein the motor may run in the second control modeat a second static pressure, which may be greater than the first staticpressure.

The foregoing method may further comprise: receiving a user's input of adesired level of airflow, wherein the user selects one of a plurality ofpredetermined levels of airflow; and retrieving the first target valuefrom a plurality of values stored in a memory of the system, wherein theretrieved first target value may be associated with the user'sselection. The method may further comprise: receiving a user's input ofa desired level of airflow, wherein the user inputs the desired levelrepresented in a number rather than selecting from preprogrammedchoices; and computing the first target value using the number and apreprogrammed formula. The first target value may be computed using arated electric current and a rated rotational speed of the motor. Themethod may further comprise receiving a user's input of a desiredmaximum rotational speed, which becomes the second target value for thesecond control mode

The motor may be coupled with a fan, which blows air in a ventilationduct, wherein running the motor in the first control mode may generatean airflow with a substantially constant airflow rate while a staticpressure within the duct significantly changes. The motor may be coupledwith a fan, which blows air in a ventilation duct, wherein the systemmay not comprise an airflow rate sensor for detecting an airflow rategenerated by the fan, wherein running the motor in the first or secondcontrol mode does not use an input of an airflow rate generated by thefan. The motor may be coupled with a fan, which blows air in aventilation duct, wherein the system may not comprise a static pressuresensor for detecting a static pressure within a ventilation duct,wherein running the motor in the first or second control mode does notuse an input of a static pressure within the ventilation duct. Runningthe motor in at least one of the first and second control nodes maycomprise adjusting a turn-on period of the motor so as to make theproduct reach the first target value. The method may further comprise:monitoring the electric current applied to the motor; and monitoring arotational speed of the motor.

Another aspect of the invention provides a method of operating anelectric motor in a ventilation system. The method comprising: running amotor in a first control mode, which attempts to make a I·RPM valuereach a first target value, wherein the I·RPM value may be a product ofan electric current and the rotational speed of the motor; monitoringchanges of the electric current; comparing the monitored electriccurrent against a reference; and transitioning the motor's operation toa second control mode, which attempts to make the rotational speed reacha second target value, when determining that the electric currentchanges from a value greater than the reference to a value smaller thanthe reference.

A further aspect of the invention provides a method of operating anelectric motor in a ventilation system. The method comprising: running amotor in a second control mode, which attempts to make a rotationalspeed of the motor reach a second target value; monitoring changes ofthe electric current; comparing the monitored electric current against areference; transitioning the motor's operation to a first control mode,which attempts to make the a I·RPM value reach a first target value,when determining that the electric current changes from a value smallerthan the reference to a value greater than the reference, wherein theI·RPM value may be a product of an electric current and the rotationalspeed of the motor.

A further aspect of the invention provides a method of operating anelectric motor in a ventilation system the method comprising: providinga user interface configured to receive a user's input; receiving auser's input of a desired level of airflow rate, wherein the desiredlevel may be a fraction of a maximum airflow rate computed using atleast one rated value of the motor; obtaining a target valuecorresponding to the desired level for a feedback control; andconducting the feedback control using the target value for asubstantially constant airflow rate.

In the foregoing method, receiving the user input may comprise receivinga user's selection among a plurality of predetermined levels. Obtainingthe target value may comprise retrieving the target value from aplurality of values stored in a memory, wherein the retrieved targetvalue may be associated with the user's selection. The desired level maybe a user inputted number rather than a selection among preprogrammedchoices. Obtaining the target value may comprise computing the targetvalue using the number and a preprogrammed formula. The feedback controlmay be to adjust a product of an electric current and a rotational speedso as to make the product stay within proximity of the target value. Thefeedback control may be conducted when an electric current applied tothe motor is greater than a reference value. The reference value may bethe same fraction of a rated electric current of the motor. The maximumairflow rate may be a product of a rated electric current and a ratedrotational speed.

The method may further comprise: receiving a user's input of a desiredlevel of a rotational speed, which may be a fractional value of a ratedrotational speed of the motor; and obtaining a target rotational speedcorresponding to the desired level for another feedback control. Themethod may further comprise conducting the other feedback control usingthe target rotational speed to make a rotational speed of the motor staywithin proximity of the target rotational speed. The other feedbackcontrol using the target rotational speed may generate a substantiallyconstant airflow rate. The other feedback control may be conducted whenan electric current applied to the motor may be smaller than a referencevalue.

The user input of a desired level may comprise a selection among aplurality of predetermined levels of rotational speed, and whereinobtaining the target rotational speed may comprise retrieving, from amemory, the target rotational speed associated with the user'sselection. The user input of a desired level may comprise a userinputted number rather than a section among preprogrammed levels, andwherein obtaining the target rotational speed may comprise computing thetarget rotational speed using the number and a preprogrammed formula.The target rotational speed may be computed using the user inputtednumber and a rated rotational speed of the motor.

A still further aspect of the invention provides a method of operatingan electric motor in a ventilation system. The method comprising:providing a user interface configured to receive a user's input;receiving a user's input of a desired level of a rotational speed, whichmay be a fractional value of a rated rotational speed of the motor; andobtaining a target rotational speed corresponding to the desired levelfor a feedback control; and conducting the feedback control using thetarget rotational speed for a substantially constant airflow rate in arange of an electric current, which may be smaller than a referencevalue.

The method may further comprise receiving a user's input of a desiredlevel of airflow rate, wherein the desired level may be a fraction of amaximum airflow rate computed using at least one rated value of themotor. The reference value may be a product of the fraction and a ratedelectric current of the motor. Conducting the feedback control using thetarget rotational speed attempts to make a rotational speed of the motorstay within proximity of the target rotational speed. The user input ofa desired level may comprise a selection among a plurality ofpredetermined levels of rotational speed, and wherein obtaining thetarget rotational speed may comprise retrieving, from a memory, thetarget rotational speed associated with the user's selection. The userinput of a desired level may comprise a user inputted number rather thana section among preprogrammed levels, and wherein obtaining the targetrotational speed may comprise computing the target rotational speedusing the number and a preprogrammed formula. The target rotationalspeed may be computed using the user inputted number and a ratedrotational speed of the motor.

A still further aspect of the invention provides a method of controllingan electric motor for use in a ventilation system. The methodcomprising: providing a ventilation system comprising a blower and aduct with at least one opening, the blower comprising a motor and a fancoupled to the motor, the blower being configured to generate an airflowthrough the at least one opening; conducting a test operation of theblower for collecting data indicative of the motor's operation in theventilation system; processing the data collected from the testoperation to generate a correction coefficient; and conducting afeedback control using a target value, which has been modified using thecorrection coefficient.

In the foregoing method, the test operation may be conducted under acondition where a static pressure inside the duct may be substantiallythe minimum. The test operation may be conducted under a condition wherethe at least one opening may be substantially fully open. Conducting thetest operation may comprise: running the motor; changing the rotationalspeed of the motor; and monitoring the electric current while changingthe rotational speed. Changing the rotational speed may comprisegradually increasing or decreasing the rotational speed. The collecteddata may comprise a relationship between an electric current applied tothe motor and the motor's rotational speed monitored during at leastpart of the test operation. Processing the data may comprise: computingvalues of the correction coefficient using an electric current and arotational speed collected during at least part of the test operation;and associating each value of the correction coefficient with avolumetric airflow rate. The method may further comprise: storing thevalues of the correction coefficient and associated volumetric airflowrates in a memory.

Still in the foregoing method, the target value may be associated with avolumetric airflow rate and has been modified using the correctioncoefficient that may be associated with the same volumetric airflowrate. The target value for the feedback control would have beendifferent unless modified using the correction coefficient. Conducting afeedback control may comprise a constant I·RPM control, which attemptsto make a product of an electric current and a rotational speed withinproximity of the target value. The target value of the feedback controlmay be a fraction of a product of a rated electric current and a ratedrotational speed, which has been modified using the correctioncoefficient. The constant I·RPM control may be conducted in a range ofelectric current, which is greater than a reference current value. Thereference current value may be a fractional value of a rated electriccurrent of the motor.

Still in the foregoing method, conducting a feedback control maycomprise: receiving a user input of a desired level of airflow rate; andcomputing the target value that corresponds to the desired level and maybe modified based on the correction coefficient. Conducting a feedbackcontrol may comprise a constant RPM control, which attempts to make arotational speed within proximity of the target value. The target valueof the feedback control may be a fraction of a rated rotational speed ofthe motor, which has been modified using the correction coefficient. Themethod may further comprise receiving a user's input of a desiredrotational speed, which becomes the target value. The correctioncoefficient may be to compensate at least some variations caused by themotor's unique relationship between an electric current applied to themotor and a rotational speed of the motor. The feedback control maygenerate a substantially constant airflow rate while a static pressurewithin the duct significantly changes. The system may not comprise anairflow rate sensor for detecting an airflow rate generated by theblower, wherein the feedback control does not use an input of an airflowrate generated by the blower. The system may not comprise a staticpressure sensor for detecting the static pressure within the duct,wherein the feedback control does not use an input of a static pressurewithin the duct.

A further aspect of the invention provides a motor control apparatus fora ventilation system. The apparatus comprises: an electric currentsensor configured to detect an electric current applied to a motor; aspeed sensor configured to detect a rotational speed of the motor; and acontroller configured to conduct a feedback control of adjusting aproduct of the electric current and the rotational speed to stay withinproximity of a target value.

In the foregoing apparatus, the controller may be further configured tocompare the electric current against a reference value, and to conductthe feedback control when the electric current is greater than thereference value. The controller may be further configured to compare theelectric current against a reference value, and to conduct anotherfeedback control of adjusting the rotational speed stay within proximityof a second target value when the electric current is smaller than thereference value. The controller may be further configured to compare theelectric current against a reference value, and to transition between afirst control mode and a second control mode based on the comparison,wherein in the first control mode the controller may be configured toconduct the feedback control, wherein in the second control mode thecontroller may be configured to conduct another feedback control ofadjusting the rotational speed stay within proximity of another targetvalue.

The foregoing apparatus may further comprise at least one user inputinterface configured to receive a user's desired level of airflow rateand to further receive a user's desired level of rotational speed. Thecontroller may be further configured to use the user's desired level ofairflow rate for the feedback control and to use the user's desiredlevel of rotational speed for another feedback control. At least one ofthe feedback control and the other feedback control may be designed toachieve a substantially constant airflow rate in different staticpressure ranges.

The controller may be further configured to control the motor'soperation so as to generate a substantially constant airflow rate from afan coupled with the motor, wherein the controller may not require aninput of the static pressure for the feedback control. The controllermay be further configured to control the motor's operation so as togenerate a substantially constant airflow rate from a fan coupled withthe motor, wherein the controller may not require an input of theairflow rate generated by the fan for eh feedback control. Thecontroller may be further configured to conduct a test operation tocollect a relationship between the electric current and the rotationalspeed, wherein the controller may be further configured to compute acorrection coefficient using the collected relationship, wherein thecontroller may be further configured to modify a target value for afeedback control using the correction coefficient.

A further aspect of the invention provides a motor control apparatus fora ventilation system. The apparatus comprises: an electric currentsensor configured to detect an electric current applied to a motor; aspeed sensor configured to detect a rotational speed of the motor; and acontroller configured to compare the electric current against areference value, and to conduct a feedback control of adjusting therotational speed stay within proximity of a second target value when theelectric current may be smaller than the reference value.

A further aspect of the invention provides a motor control apparatus fora ventilation system. The apparatus comprises: an electric currentsensor configured to detect an electric current applied to a motor; aspeed sensor configured to detect a rotational speed of the motor; and acontroller configured to compare the electric current against areference value, and to transition between a first control mode and asecond control mode based on the comparison, wherein in the firstcontrol mode the controller may be configured to adjust a product of theelectric current and the rotational speed to stay within proximity of afirst target value, wherein in the second control mode the controllermay be configured to adjust the rotational speed stay within proximityof a second target value.

A further aspect of the invention provides a motor control apparatus fora ventilation system. The apparatus comprises: an electric currentsensor configured to detect an electric current applied to a motor; aspeed sensor configured to detect a rotational speed of the motor; atleast one user input interface configured to receive a user's desiredlevel of airflow rate and to further receive a user's desired level ofrotational speed; and a controller configured to use the user's desiredlevel of airflow rate for a first control mode and to use the user'sdesired level of rotational speed for a second control mode.

A further aspect of the invention provides a motor control apparatus fora ventilation system. The apparatus comprises: an electric currentsensor configured to detect an electric current applied to a motor; aspeed sensor configured to detect a rotational speed of the motor; and acontroller configured to control the motor's operation so as to generatea substantially constant airflow rate from a fan coupled with the motor,wherein the controller may be configured to accomplish the substantiallyconstant airflow rate over a significant range of a static pressure in aduct in which the blower may be installed without an input of the staticpressure. The system may not comprise a static pressure sensor fordetecting the static pressure in the duct.

A further aspect of the invention provides a motor control apparatus fora ventilation system. The apparatus comprises: an electric currentsensor configured to detect an electric current applied to a motor; aspeed sensor configured to detect a rotational speed of the motor; and acontroller configured to control the motor's operation so as to generatea substantially constant airflow rate from a fan coupled with the motor,wherein the controller may be configured to accomplish the substantiallyconstant airflow rate over a significant range of a static pressure in aduct in which the blower may be installed without an input of theairflow rate generated by the fan. The system may not comprise anairflow rate sensor for detecting the airflow rate generated by the fan.

A further aspect of the invention provides a motor control apparatus fora ventilation system. The apparatus comprises: an electric currentsensor configured to detect an electric current applied to a motor; aspeed sensor configured to detect a rotational speed of the motor; and acontroller configured to conduct a test operation to collect arelationship between the electric current and the rotational speed,wherein the controller may be further configured to compute a correctioncoefficient using the collected relationship, wherein the controller maybe further configured to modify a target value for a feedback controlusing the correction coefficient.

In the foregoing apparatus, the controller may be further configured togradually change the rotational speed of the motor and monitor theelectric current to collect the relationship. The controller may befurther configured to generate values of the correction coefficient forvarious airflow rates. The controller may be configured to modify thetarget value at a given airflow rate using a value of the correctioncoefficient corresponding to the given airflow rate.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings include:

FIG. 1 illustrates a constant airflow operation and a non-constantairflow operation in a ventilation system while static pressure inside aduct changes;

FIG. 2 illustrates a typical relationship between static pressure andmotor's speed (RPM) in a constant airflow operation;

FIG. 3 is a block diagram of a motor control system according to oneembodiment;

FIG. 4 is a flow chart for a constant I·RPM motor control operationaccording to one embodiment;

FIG. 5 illustrates a RPM-static pressure profile in a motor controloperation according to one embodiment;

FIG. 6 is a flowchart of a motor control operation including atransition between a constant I·RPM control and a constant RPM controlaccording to one embodiment;

FIG. 7 illustrates an RPM-static pressure relationship in multi-levelairflow controls according to one embodiment;

FIG. 8 illustrates a static pressure-airflow rate relationship inmulti-level airflow controls according to one embodiment;

FIG. 9 is a flowchart for a test operation and a modified constantairflow control using data from the test operation according to oneembodiment;

FIG. 10 illustrates a current-RPM characteristic of a motor acquired ina test operation according to one embodiment;

FIG. 11 illustrates a Kr-RPM relationship of a motor according to oneembodiment;

FIG. 12 illustrates an RPM-airflow rate relationship in a steady stateoperation of a motor when the static pressure remains constant accordingto one embodiment;

FIG. 13 illustrates a Kr-airflow rate relationship of a motor accordingto one embodiment;

FIG. 14 is a detailed block diagram of a motor controller for aventilation system according to one embodiment;

FIG. 15 is a circuit diagram of the motor controller of FIG. 14;

FIG. 16 is a circuit diagram of a speed control interface circuit shownin FIG. 14; and

FIGS. 17A and 17B illustrate a PWM input signal and a conversed PWMsignal for use in a motor speed control according to one embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

Various embodiments of the invention will be discussed in more detailbelow, with reference to the drawings. The sizes and shapes of elementsshown in the drawings do not represent actual sizes or shapes, norrepresent relative sizes of the elements shown in a single drawing.

Static Pressure Changes in a Ventilation System

As discussed above in the Background section, a ventilation systemtypically includes a motor, a fan coupled to the motor and a ventilationduct to guide air blown by the fan. The pressure inside the ventilationduct (static pressure) changes for many reasons. The static pressureinside the duct changes, for example, when an object is placed insidethe duct or in front of an opening of the duct. Dust accumulated withinthe duct or in a filter installed in the duct can increase the staticpressure inside the duct. The static pressure changes make the airflowcontrol difficult. In particular, the static pressure changes in theduct influence the operation of the motor.

Motor Controller

In embodiments, a motor control circuit or controller controls operationof the motor for adjusting the air flow rate in a ventilation system.More specifically, the controller controls the operation of the motor togenerate a substantially constant airflow rate in the duct. In oneembodiment, the controller controls the motor operation to generate asubstantially constant airflow rate over static pressure changes in theduct of the ventilation system. The controller may not require a staticpressure sensor for monitoring the static pressure changes or a feedbackcontrol based on a monitored static pressure input. Also, the controllermay not require an airflow rate sensor for monitoring the airflow ratechanges or a feedback control based on a monitored airflow rate input.In some embodiments the controller are imbedded in the motor, and inothers the controller is separate from the motor.

In one embodiment, the controller or its associated sensor monitors therotational speed (e.g., RPM) of the motor and utilizes the monitoredspeed for the control of the airflow rate. In one embodiment, thecontroller or its associated sensor monitors the electric currentapplied to the motor and utilizes the monitored electric current for thecontrol of the airflow rate. As will be discussed in detail, in oneembodiment, the controller processes the rotational speed input and theelectric current input so as to determine the length of time duringwhich the power is turned on (i.e., turn-on period) to accomplish asubstantially constant airflow. In this embodiment, the controllercontrols the airflow rate using intrinsic information of the motor'soperation, such as rotational speed and electric current, rather thanusing extrinsic information such as static pressure and airflow rate.

Substantially Constant Airflow

FIG. 1 plots changes of the airflow rate (volume/time) over changes ofstatic pressure in a ventilation duct. Line 20 represents a constantairflow control of the motor operation according to an embodiment of theinvention. Line 22 represents non-controlled operation of a motor, inwhich the airflow rate decreases as the static pressure increases. Inthe constant airflow control line 20, the airflow rate, e.g., in CFM(cubic feet per minute) stays substantially constant over significantchanges in the static pressure. In other words, the airflow rate remainswithin a range between a lower limit QL and a higher limit QH regardlessthe change of the static pressure.

According to embodiments of the invention, the controller attempts tocontrol the motor's operation such that the airflow rate changes likethe constant airflow control line 20 at least for a static pressurerange. As a result when the motor operates under the constant airflowcontrol, the airflow rate stays substantially constant for at least partof the span of static pressure changes or throughout the span of thestatic pressure changes.

Here, a substantially constant airflow means that the airflow rateremains within a range as the static pressure changes. According tovarious embodiments, the range for a substantially constant airflow ratecan be about 2, 4, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28 or 30percent of the total range in which the airflow rate can change whenthere is no airflow control. Alternatively, the range for asubstantially constant airflow rate can be about 1, 3, 7, 9, 11, 13, 15,17, 19, 21, 23, 25, 27 or 29 percent of the range of the airflow ratesbetween 0 CFM and the maximum airflow rate the motor can generate in agiven ventilation system.

Alternatively, a substantially constant airflow means that the airflowrate is within proximity of a target value as the static pressurechanges. According to various embodiments, the airflow rate is withinproximity of a target value when the airflow rate is within about 2, 4,8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28 or 30 percent of the totalspan of the airflow rate. Alternatively, “within proximity” isaccomplished when the airflow rate is within about 1, 3, 7, 9, 11, 13,15, 17, 19, 21, 23, 25, 27 or 29 percent of the range of the airflowrates between 0 CFM and the maximum airflow rate the motor can generatein a given ventilation system.

FIG. 2 illustrates a typical relationship between a motor's RPM and thestatic pressure changes in a duct when substantially constant airflow isaccomplished and maintained throughout the static pressure range. In thestatic pressure range 25 a between the minimum static pressure and amidpoint 25 c, the motor's RPM changes significantly as the staticpressure changes. On the other hand, the static pressure range 25 bbetween the midpoint 25 c and the minimum static pressure, the motor'sRPM changes significantly less than in the range 25 a as the staticpressure changes. In one embodiment, the controller uses the motor's RPMand the electric currently applied to the motor to control the motoroperation and emulate the relationship illustrated in FIG. 2.

Constant Airflow Control

In a ventilation system having an outlet with a variable opening area,an airflow rate (Q) can be represented by Formula 1 below, in which “A”denotes the open area of the outlet and “V” denotes the speed of the airpassing the outlet.Q=A×V  (1)

The open area (A) of the outlet has a generally direct relationship witha load applied to the motor. As the open area (A) of the outletincreases, the load applied to the motor generally proportionallyincreases. Assuming all other conditions remain the same, an increase ofthe load increases the electric current (I) applied to the motor. Thus,the open area (A) of the outlet and the electric current (I) applied tothe motor have the general relationship of Formula 2.I∝A  (2)

The speed of air (V) passing the outlet opening is generallyproportional to the motor's rotational speed (e.g., RPM), assuming allother conditions remain the same. Thus, the motor's RPM and the speed(V) of air have the general relationship of Formula 3.RPM∝V  (3)

In view of the foregoing relationships, the airflow rate (Q) of aventilation system can be represented using the electric current (I) andthe motor's speed (RPM) as in Formula 4, in which “α” is a constantcoefficient.Q=α·I·RPM  (4)

As noted above, a constant airflow control is to maintain the airflowrate (Q) constant or substantially constant. Thus, in theory, theconstant airflow control can be accomplished by maintaining the productof the electric current (I) and the motor's speed (RPM) to stay constantwhile running the motor. This relationship is represented in Formula 5.I·RPM=constant  (5)

The relationship of Formula 5 is used in some embodiments of theinvention. The foregoing discussion to reach Formula 5 provides somescientific and practical relationship among the variables (Q, A, V, RPMand I) in the ventilation system. However, their representations may notbe exact in actual ventilation systems. As such, the present inventionand its embodiments are not bound by any theory, even including theforegoing discussion to arrive in Formula 5.

Constant I·R Control

According to various embodiments, a motor control system controls theoperation of the motor such that the I·RPM value remains constant orsubstantially constant. Here, a substantially constant I·RPM means thatthe product of the electric current and the motor's speed remains withina range as the static pressure changes. The range for a substantiallyconstant I·RPM can be about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 percent of thetotal range in which the motor's I·RPM can change. Optionally the rangeis about 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 or 6 of the totalI·RPM range. Alternatively, the I·RPM range can be about 1, 2, 3, 4, 5,6, 7, 8, 9 or 10 percent of the product of the rated speed (RPM₀) andrated current (I₀) of the motor. Optionally the range is about 0.5, 1,1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 or 6 percent of the product(I₀·RPM₀).

In certain embodiments, the motor control system conducts a feedbackcontrol of the motor operation. In one embodiment, the feedback controlattempts to make the I·RPM value reach a target value. During thefeedback control, the I·RPM value changes in the vicinity of the targetvalue. In another embodiment, the feedback control makes the I·RPM valuestay within proximity of a target value. Here, the I·RPM value is in thevicinity or within proximity of a target value when the I·RPM value at agiven time is apart from the target value by less then about 1, 2, 3, 4,5, 6, 7, 8, 9, 10 percent of the total range in which the motor's I·RPMcan change. Optionally the proximity range is less than about 0.5, 1,1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 or 6 of the total I·RPM range.Alternatively, the I·RPM value is within proximity of a target valuerange when the I·RPM value at a given time is apart from the targetvalue by less then about 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 percent of theproduct of the rated speed (RPM₀) and rated current (I₀) of the motor.Optionally the proximity range is less than about 0.5, 1, 1.5, 2, 2.5,3, 3.5, 4, 4.5, 5, 5.5 or 6 percent of the product (I₀·RPM₀).

To implement this control, referring to FIG. 3, the motor control systemincludes a current sensor 301, a speed sensor 303, a controller 305 anda motor 307. The current sensor 301 detects and monitors the electriccurrent (I) applied to the motor 307. Also, the speed sensor 303 detectsand monitors the rotational speed (RPM) of the motor 307. These sensors301, 303 and/or the controller 305 can be implemented within the motorhousing or outside.

FIG. 4 is a flow chart for the motor control operation in accordancewith one embodiment. In step 401, the controller 305 receives theelectric current (I) and the motor speed (RPM) from the current sensor301 and speed sensor 303. In one embodiment, the electric current (I)and the motor speed (RPM) are tagged with the time of sensing. For thispurpose, in one embodiment, the current sensor 301 and speed sensor 303are synchronized. In one embodiment, the electric current (I) and themotor speed (RPM) are substantially continuously supplied to thecontroller 305. In one embodiment, the electric current (I) and themotor speed (RPM) are supplied to the controller 305 periodically orsporadically.

Then, the controller 305 processes the inputs and generates a controlsignal to control the motor's operation. In step 403, the controller 305calculates the I·RPM value by multiplying the inputted electric current(I) and the motor speed (RPM) that are detected at the same time. IN thealternative, the controller 305 may obtain an equivalent value of theI·RPM value (e.g., I·RPM value multiplied by a coefficient). Following,in step 405, the controller 305 compares the resulting value against atarget constant value for the constant airflow control so as to obtain adifference between them. In one embodiment, the target constant value ispredetermined or preprogrammed. In another embodiment, the targetconstant value is chosen during the operation using the I·RPM values ofearlier time of the same operation.

Subsequently in step 407, the controller 305 generates a control signalto compensate the difference obtained in the previous step. In oneembodiment, the control signal specifies the length of period duringwhich the electric current is applied to the motor, i.e., the power ison. To compensate varying values of the difference, the controller 305changes the length of period, which in turn changes the speed of themotor. The length of the period has generally proportional relationshipwith the speed of the motor. Thus, when the controller 305 generates acontrol signal specifying a longer period, the speed of the motorincreases, vice versa. In one embodiment, the length of period isrepresented in a pulse width using a pulse width modulation (PWM). Inanother embodiment, the controller uses a method other than the PWM.Also, in other embodiments, the control signal specifies one or moreother variables to compensate the electric difference obtained in theprevious step.

The foregoing control for a constant I·RPM value can provide asubstantially constant airflow through the ventilation outlet. Thesubstantially constant airflow can be obtained throughout the span ofthe static pressure or in at least only part of the span of the staticpressure. The relationship between the motor's RPM and static pressurefrom this constant I·RPM control is similar to the profile of FIG. 2 inat least part of the static pressure span. Thus, using the constantI·RPM control, a substantially constant airflow can be achieved over thechanges of the static pressure.

In the discussed embodiments, the constant airflow control is performedover a range of static pressure changes without the need of a staticpressure sensor for monitoring the static pressure and without afeedback control using an input of static pressure. Further, theconstant airflow control is performed over a range of static pressurechanges without the need of an airflow rate sensor for monitoring theairflow rate in the duct or outlet and further without a feedbackcontrol using an input of airflow rate.

In certain conditions, the constant I·RPM control provides a betterresult in some static pressure ranges than others. Thus, while in someembodiment, the constant I·RPM control is used throughout the staticpressure range; in other embodiment, the constant I·RPM control only ina certain static pressure range. In one embodiment, the constant I·RPMcontrol is used in a lower static pressure range as in the range 25 a ofFIG. 2, which generally corresponds to a higher electric current.

In one embodiment, the constant I·RPM control is used when the electriccurrent is higher than a value, which is predetermined or chosen duringthe operation. In another embodiment, the constant I·RPM control is usedwhen the electric current is within a range. In another embodiment, theconstant I·RPM control is used in a higher static pressure range as inthe range 25 a of FIG. 2, which corresponds to a lower electric current.In another embodiment, the constant I·RPM control is used when theelectric current is lower than a value, which is predetermined or chosenduring the operation.

Constant RPM Control

In some ventilation systems, the constant I·RPM control may not verywell emulate the relationship illustrated in FIG. 2 in certain staticpressure range. It is particularly true in the high static pressurerange 25 b, in which the motor's speed changes much less than thechanges of the static pressure. Thus, in one embodiment, the controller305 runs in a constant RPM control mode, in which the motor's rotationalspeed (e.g., RPM) stays constant or substantially constant in the highstatic pressure range 25 b. Here, a substantially constant RPM meansthat the motor's RPM remains within a range as the static pressurechanges. The range for a substantially constant RPM can be about 1, 2,3, 4, 5, 6, 7, 8, 9, 10 percent of the total range in which the motor'sRPM can change. Optionally the range is about 0.5, 1, 1.5, 2, 2.5, 3,3.5, 4, 4.5, 5, 5.5 or 6 of the total RPM range. Alternatively, the RPMrange can be about 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 percent of the ratedspeed (RPM₀) of the motor. Optionally the range is about 0.5, 1, 1.5, 2,2.5, 3, 3.5, 4, 4.5, 5, 5.5 or 6 percent of the rated speed (RPM₀) ofthe motor.

In embodiments, the motor controller conducts a feedback control of themotor operation to achieve the constant RPM control. In one embodiment,the feedback control attempts to make the motor's rotational speed reacha target value. During the feedback control, the rotational speedchanges in the vicinity of the target value. In another embodiment, thefeedback control makes the rotational speed stay within proximity of atarget value. Here, the rotational speed is in the vicinity or withinproximity of a target value when its value at a given time is apart fromthe target value by less then about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10percent of the total range in which the motor's rotational speed canchange. Optionally the proximity range is less than about 0.5, 1, 1.5,2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 or 6 of the total range of the rotationalspeed. Alternatively, the rotational speed is within proximity of atarget value range when its value at a given time is apart from thetarget value by less then about 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 percentof the rated rotational speed (RPM₀) of a particular motor. Optionallythe proximity range is less than about 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4,4.5, 5, 5.5 or 6 percent of the rated rotational speed (RPM₀).

Referring to FIG. 5, line 23 b represents this constant RPM control inthe static pressure range 25 b. In one embodiment, the constant RPMcontrol is applied to only part of the range 25 b. In the constant RPMcontrol embodiments, maintaining the motor's speed constant creates asubstantially constant airflow although that control may not exactlyemulate the profile in FIG. 2. Also, maintaining the motor's speedconstant may at least achieve a result in which the airflow rate stayswithin a range, which is wider than narrow. The constant RPM control isvery useful in ventilation systems, which do not require a strictconstant airflow control in a high static pressure range.

Transition between Constant I·RPM Control and Constant RPM Control

In FIG. 5, the line 23 b represents the constant RPM control, and theline 23 a represents the constant I·RPM control. As indicted in FIGS. 2and 5, the static pressure is generally inversely proportional to theload applied to the fan and motor. Given that the load is generallyproportional to the current, the transition between the two controls canbe determined based on the electric current (I). In one embodiment, whenthe electric current is smaller than a reference electric current, theconstant RPM control is chosen; and when the electric current is greaterthan the reference electric current, the constant I·RPM control is used.As such, the transitional point 24 is found without an input of thestatic pressure. The values of the reference electric current will bediscussed below.

Multi-Level and Programmable Constant I-R Control

In one embodiment, the motor control system provides a multi-levelconstant airflow control, which allows users to choose a target airflowrate from multiple predetermined airflow rates. Each of thepredetermined airflow rates is associated with a target value for theconstant airflow control. In this embodiment, when a user selects one ofthe predetermined airflow rates, the controller feedback-controls theoperation of the motor such that the product of the I·RPM value or itsequivalent reaches and stays at about the target value associated withthe user selected airflow rate.

In one embodiment, the target values associated with the multipleairflow rates are predetermined with reference to a maximum hypotheticalI·RPM value, which corresponds to a maximum hypothetical airflow rateavailable from the ventilation system. In one embodiment, the maximumhypothetical I·RPM value refers to the I·RPM value obtained using themotor's rated current (I₀) and rated RPM (RPM₀) as in Formula 6.Maximum hypothetical I·RPM value=I ₀ ·RPM ₀  (6)

In one embodiment, the target values associated with the multipleairflow rates are predetermined with reference to a maximum hypotheticalI·RPM value, which corresponds to a maximum hypothetical airflow rateavailable from the ventilation system. In one embodiment, the maximumhypothetical I·RPM value refers to the I·RPM value obtained using themotor's rated current (I₀) and rated RPM (RPM₀) as in Formula 6.

In one embodiment, each target value is a fraction or percentage of themaximum value obtained using Formula 6 or other appropriate formulas.Then, each airflow rate associated with the target value generallyrepresents a corresponding fraction of the maximum hypothetical airflowrate available from the motor. Table 1 is an example listing airflowrates and associated target values that are stored in the controller 305or an associated memory, in which the motor's maximum hypothetical I·RPMvalue is 20.

TABLE 1 Airflow Rate Levels Associated Target Values 20% 4 40% 8 60% 1280% 16 100% 20

Alternatively or additionally, in one embodiment, the motor controlsystem provides a user programmable constant airflow control, in whichusers are allowed to input a desired airflow rate or level rather thanselecting one of preprogrammed airflow rates or levels. For example, auser inputs 35% level of constant airflow control, the controller 305computes a target value for the 35% level, which is 35% of the maximumhypothetical I·RPM value of the motor. Then, the controller 305 controlsthe operation of the motor such that the I·RPM value can reach and stayat the value of 35% of I₀·RPM₀.

In these embodiments with multi-level and/or programmable constantairflow control, the system includes an appropriate user interface orcontrol panel, with which users can select or input a desired airflowrate level. Further, these embodiments optionally include an appropriateindicator or display device to indicate or display the presently chosenairflow rate level.

Reference Electric Current for Transition between Controls

As discussed above, in one embodiment, the transition between theconstant I·RPM control and the constant RPM control is determined basedon the electric current applied to the motor. More specifically, thereference electric current differs in different airflow rate levels. Inone embodiment, the reference electric current is predetermined orcalculated using the rated electric current (I₀) of the motor. Forexample, the reference electric current for a certain percent airflowrate has a value of the same fraction of the rated electric current.

Table 2 is an example listing airflow rates and associated referenceelectric current for transitioning between the constant RPM control andthe constant I·RPM control.

TABLE 2 Airflow Rate Levels Reference Electric Current 30% 0.3 × I₀ 50%0.5 × I₀ 70% 0.7 × I₀ 90% 0.9 × I₀ 100% I₀Multi-Level and Programmable Constant RPM Control

In one embodiment, the motor control system provides a multi-levelconstant speed (RPM) control, which allows users to choose a targetspeed value from multiple predetermined speed values. Alternatively oradditionally, in one embodiment, the motor control system provides auser programmable constant RPM control, in which users are allowed toinput a desired RPM value or level rather than selecting one ofpreprogrammed RPM values.

In one embodiment, the target RPM values are predetermined withreference to the rated RPM (RPM₀) of a motor or another reference RPMvalue. In one embodiment, each target RPM value is a percentage orfractional level of the rated RPM (RPM₀) or the other reference value.In these embodiments, in a percentage level is chosen or inputted by auser for the performance of the constant RPM control at an RPMcorresponding to the percentage level.

In these embodiments with multi-level and/or programmable constant RPMcontrol, the system includes an appropriate user interface (notillustrated) or control panel (not illustrated), with which users canselect or input a desired airflow rate level. The feature of userselection or programming of the motor speed is particularly useful totechnicians who have developed certain senses about the correlationbetween the motor's speed and airflow rates. These technicians andexperts could find a good approximation about the motor's speed toaccomplish a desired airflow rate, which can be inputted to the motorcontrol system for the constant RPM control. Further, these embodimentsoptionally include an appropriate indicator or display device toindicate or display the presently chosen airflow rate level.

Overall Process for Constant Airflow Control

FIG. 6 is a flowchart of the process of constant airflow controlaccording to an embodiment. In step 601, a user selects or inputs adesired level of airflow rate for a constant airflow control using auser interface or a control panel of the motor or motor controller 305.In one embodiment, the selection or input of the desired level sets adesired airflow rate for the constant I·RPM control and also for theconstant RPM control. In another embodiment, the desired leveldetermines the desired airflow rate for the constant I·RPM control, andthe user may need to provide a desired level of motor speed for theconstant RPM control. Thus, optionally, in step 603 the user selects orinputs a desired level of motor speed, which may occur prior to step 601in some embodiments.

Then, the user turns on and runs the motor. After a transient period fora certain rotational speed, in step 605 the controller 305 compares theelectric current (I) to the reference electric current calculated basedon the desired level of airflow rate. For example, in case the inputteddesired level is 70%, the reference electric current is 70% of the ratedelectric current of the motor. In this comparison, if the electriccurrent applied to the motor is greater than the reference electriccurrent, the controller 305 selects the constant I·RPM control 607. Onthe other hand, if the electric current applied to the motor is smallerthan the reference electric current, the controller 305 selects theconstant RPM control 609. In one embodiment, during the operation, thecontroller 305 goes to step 605 and conducts the comparison constantlyto determine whether to transition from one control to the other.Alternatively, the comparison of step 605 can be conducted periodicallyor sporadically to determine the need for transition between thecontrols.

FIG. 7 illustrates the relationship between the motor speed (RPM) andstatic pressure in multi-level constant airflow controls, includingthree profiles similar to FIG. 5. The profile A represents 10% level ofairflow rate control; the profile B represents 50% level; and theprofile C represents 70% level. Each profile includes a constant RPMcontrol section in the static pressure range from the maximum to amidpoint referred to as constant rate point (CRP). Also, each profiletransitions to a constant I·RPM control in the static pressure rangefrom the midpoint to the minimum static pressure. FIG. 8 illustrates therelationship between the static pressure and the airflow rate in themulti-level constant airflow controls corresponding to FIG. 7. InProfile C, the portion 801 corresponds to the higher static pressurerange in which the constant RPM control is conducted; and the portion803 corresponds to the lower static pressure range in which the constantI·RPM control is conducted.

Correction of Motor Output Variations

Motors produced with the identical design and manufacturing may not havethe identical operating characteristics. Also, motors produced in thesame batch may have slight differences in their responses to certaincontrols. Further, a single motor can have different responses to thesame control action when the motor operates under different contexts,such as different designs (size, weight, configurations, etc.) of thefan coupled with the motor and different designs of the ventilation duct(size and configurations). The results of these are deviations andvariations from a computed output when a control action is taken. In theconstant I·RPM control or the constant RPM control, for example, themotor's response to a control action to achieve a target value canresult in a slight deviation from the target value although the responseis good enough to produce a generally desired result, i.e., asubstantially constant airflow rate.

According to one embodiment, the controller 305 corrects thesevariations and deviations for better constant airflow controls. Morespecifically, the controller 305 conducts one or more test operations,and collects certain data specific to at least one of the motor, fan andduct configurations. In one embodiment, the test operation is carriedout when the motor is coupled with a particular fan and installed in aparticular ventilation duct or system. In one embodiment, the collecteddata are stored in a memory associated with the controller 305 and usedto minimize the deviations so as to accomplish that the motor operationis close to the profile of FIG. 2 for at least part of the staticpressure span. In one embodiment, the data are further processed toproduce a reduced form of data that has more direct correlation with thecontrol of the motor operation. The reduced form of data is then storedin the memory and used to achieve a desired operation of the motor for asubstantially constant airflow rate.

FIG. 9 is a flow chart of a process according to embodiments forcorrecting the motor output variations. In step 902, a test operation ofthe ventilation system is performed under its minimum static pressurecondition. During the test operation, in step 904, the electric currentapplied to the motor is monitored while changing the motor's speed(e.g., RPM). In step 906, the current and RPM data obtained from thetest operation is processed to produce a coefficient (e.g., Kr), whichcan represent deviations in the actual motor operations from itscorresponding computed value at different levels of airflow rates. Instep 908, a correction coefficient for compensating or correcting thedeviations is obtained for each airflow rate level, and in step 910 thecorrection coefficient is stored in a memory associated with thecontroller. Then, in step 912, the motor is operated for a constantairflow control, and a control target value is compensated using thestored correction coefficient values. Various features and embodimentsof the test operation and the controlled operation will be furtherdiscussed.

Test Operation

In one embodiment, the test operation is performed under the same orvery similar condition where the motor is operated for ventilation. Inthis embodiment, in order to conduct the test, the motor is assembledwith a fan and installed in the ventilation system to blow air throughthe duct. Thus, the test results from the test operation reflect theconditions of actual operation of the ventilation system, such as, size,design and weight of the fan, and the configuration of the duct.

During the test operation, the motor is operated under the minimumstatic pressure condition. The ventilation duct has one or more outletsthrough which air blown from the fan is discharged. In one embodiment,the minimum static pressure condition can be created by opening theoutlets to their maximum size. During the test operation, the motor isrun while changing the RPM by changing the length of period during whichthe electric current is applied to the motor. In one embodiment, themotor's RPM is increased and/or decreased gradually, stepwise, randomlyor in combination. In one embodiment, the motor's RPM is continuouslyand gradually increased. While changing the motor's RPM, the electriccurrent applied to the motor is monitored. In embodiments, the RPM andcurrent at each time are recorded continuously, intermittently or incombination. FIG. 10 illustrates examples of recorded current-RPMrelation for three different motors or three different conditions forthe same motor.

Processing Data from Test Operation

In step 906 of FIG. 9, the controller processes the data obtained fromthe test operation so as to produce Kr values. In one embodiment, Kr isa coefficient obtained using Formula 7, in which β is a coefficienthaving a constant value.Kr=β·I/RPM  (7)

In one embodiment, β equals to “1”, where Kr=I/RPM. The Kr valuesobtained using Formula 7 is plotted against the motor's speed in FIG.11. In one embodiment, the Kr-RPM relation as in FIG. 11 is thenconverted to the relation between Kr values and different levels ofairflow rate of the particular motor in the particular ventilationsystem. Here, the term “different levels of airflow rate” refers tovarious fractions of the maximum airflow rate of the motor. In oneembodiment, the maximum airflow rate is the airflow rate obtainable whenthe rated electric current (I₀) and rated speed (RPM₀) of the motor areachieved. Using Formula 4, the maximum airflow rate is represented withthe maximum hypothetical I·RPM value (I₀·RPM₀) in Formula 8.Q ₀ =α·I ₀ ·RPM ₀  (8)

In one embodiment, the conversion of the Kr-RPM relation to theKr-airflow rates relation can be based on the relation between RPM andairflow rates of the motor. Typically, the RPM of a motor isproportional to the airflow rate generated from the motor when thestatic pressure of the ventilation duct does not change. For example,the RPM-airflow rate relations 1201, 1202 of two motors are plotted inFIG. 12. In one embodiment, using the proportional relation between theRPM and airflow rates, the Kr-RPM relation in FIG. 11 can be convertedto the Kr-airflow rate relation. In other embodiments, the Kr-RPMrelation is converted to the Kr-airflow rate relation using a linear ornon-linear relation between the RPM and airflow rates of a particularmotor.

FIG. 13 plots the Kr-airflow rate relation converted from the Kr-RPMrelation of FIG. 11 according to one embodiment. The maximum RPM of FIG.11 corresponds to the maximum airflow rate of FIG. 13, and eachfractional level (e.g., percentage) of the maximum RPM of FIG. 11corresponds to a fractional level (e.g., percentage) of the maximumairflow rate of FIG. 13. Although FIGS. 11 and 13 plot the Kr-RPM andKr-airflow rate relations continuously, in actual embodiments theserelations may be generated discontinuously. Optionally, although notincluded in the flowchart of FIG. 9, the resulting Kr-airflow raterelation in a continuous or discrete format is stored in a memoryassociated with the controller.

In step 908 of FIG. 9, a correction coefficient is obtained for eachairflow rate or its fractional level. The correction coefficient canrepresent deviations in the actual motor operations from itscorresponding computed value at different levels of the airflow rate.Thus, the correction coefficient can be used to compensate thedeviations at different levels of the airflow rate. In one embodiment,the correction coefficient represents the size of deviation of the Krvalue from the corresponding value computed using the rated current andrated RPM. In one embodiment, the correction coefficient (γ) isrepresented by Formula 8.γ·K ₀ =Kr  (8)

In one embodiment, K₀ denotes the Kr counterpart that is computed usingthe rated current and rated RPM as in Formula 9.K ₀ =I ₀ /RPM ₀  (9)

Subsequently, in step 910, at least part of the resulting data is storedin a memory associated with the controller. The resulting data includesKr values, K₀ values, correction coefficients (γ) for various airflowrates or their fractional levels. In one embodiment, only correctioncoefficient (γ) and the corresponding airflow rate or its fractionallevel are stored in a memory. In embodiments, either or both of the Krvalues and the K₀ values are also stored in the memory. In oneembodiment, the resulting data are stored as a table, in which eachairflow rate value has a corresponding value of the correctioncoefficient (γ) and optionally other data obtained from the foregoingprocesses. Table 3 is an example listing the values of Kr, K₀ and γ foreach airflow rate.

TABLE 3 Airflow Rate Levels Kr₀ Kr γ 10% 0.1 · I₀/RPM₀ = 0.00018 0.000190.947 20% 0.2 · I₀/RPM₀ = 0.00024 0.00025 0.960 30% 0.3 · I₀/RPM₀ =0.00030 0.00032 0.938 40% 0.4 · I₀/RPM₀ = 0.00038 0.00038 1 50% 0.5 ·I₀/RPM₀ = 0.00043 0.00045 0.956 60% 0.6 · I₀/RPM₀ = 0.00062 0.000601.033 70% 0.7 · I₀/RPM₀ = 0.00075 0.00073 1.027 80% 0.8 · I₀/RPM₀ =0.00085 0.00082 1.037 90% 0.9 · I₀/RPM₀ = 0.00092 0.00091 1.011 100%   1· I₀/RPM₀ = 0.00099 0.001 0.99

According to the embodiment represented in Table 3, the airflow rate isstored as a fraction (e.g., percentage) of the maximum airflow ratealthough not limited thereto. Likewise, the Kr and K₀ valuescorresponding to airflow rates can be stored as a fraction (e.g.,percentage) of their maximum values or as their actual values calculatedfrom appropriate formulae using the data obtained during the testoperation. In other embodiments, the airflow rate levels are notrepresented in discrete numbers (e.g., 1, 2, 3 . . . N-1, N) rather thanfractions of the maximum airflow rate as also shown in FIG. 13 (see thenumbers below the horizontal line).

More Accurate Constant Airflow Control

In step 912 of FIG. 9, the controller 305 uses the data stored in thememory for a more accurate constant airflow control. In embodiments, thecorrection coefficient (γ) is factored in to produce a modified targetvalue in the constant I·RPM control or the constant RPM control. Eachcontrol changes a certain variable, such as the pulse width during whichthe electric current is applied, so as to drive the value of a formulato a target value. In certain embodiments discussed above, the targetvalues for control is obtained or computed based on the rated values,such as the rated electric current and rated speed of the motor, whichare determined from manufacturing. Now, in one embodiment, the targetvalues are adjusted or modified based on data drawn from the motor'stest operation, including the correction coefficient. More specificallythe target values are modified differently at different levels ofairflow rate.

In one embodiment of the constant I·RPM control, the target value is afraction of the hypothetical maximum I·RPM. In the embodiment, thistarget value is adjusted using the correction coefficient (γ). In oneembodiment of the constant RPM control, the target value is a fractionof the rated speed (RPM₀). In another embodiment of the constant RPMcontrol, the target value is a user inputted target RPM. In theseembodiments, the target value is adjusted using the correctioncoefficient (γ).

According to embodiments of the invention, the system provides acontroller that allows the constant airflow control at various targetairflow rates. Further, the controller provides for the adjustment ofthe constant airflow control based on the RPM and electric currentrelationship obtained from a test operation to make the control moreaccurate. These controls make the airflow rate remains substantiallyconstant irrespective of significant changes of the static pressure incertain static pressure ranges.

Response Rate Correction

In one embodiment, constant airflow controls can be further modified andimproved based on the response rate of the motor. Generally, the largeror heavier the fan coupled with the motor is, the smaller the responserate of the motor is preferred; and the smaller or lighter the fan is,the larger the response rate is preferred. In one embodiment, the systemprovides a user interface or control panel, with which the motoroperator selects or inputs a desired motor response rate. Using thisfeature, the motor operator can further improve the constant airflowcontrol to accomplish substantially constant airflow rate over thestatic pressure changes. Particularly, when the fan is replaced, anoperator or technician can set a desired response rate based on at leastone of the new fan's configuration, size and weight.

Controller Circuits

In various embodiments, the motor controller can be implemented invarious ways including both software and hardware. FIG. 14 illustratesan exemplary controller according to an embodiment of the invention. Inthe illustrated embodiment, the motor controller includes an electroniccontrol circuit 70. The electronic control circuit 70 includes a powerswitch circuit 4, a gate circuit or drives 5 and a logic circuit 6. Thepower switch circuit 4 has an output connected to a motor 2 via a line12 and supplies a motor coil with switching power, such as asingle-phase, two-phase or three-phase for driving a fan 1. The motor 2can be an electrically commutated motor (ECM) or a brushless motor (BLM)although not limited thereto. The gate circuit 5 is provided for drivingthe power switch circuit 4, and a logic circuit 6 is provided forcontrolling a control signal suitable for each motor driving method.

In the illustrated embodiment, the motor controller further includes acurrent detection circuit 8 for detecting a load current 22 flowingthrough the motor coil, and a rotor position detection processingcircuit 3 for processing a pulse of a position detection signal of amotor rotor. The current detection circuit 8 is connected to an input ofa microprocessor 7 via a line 23. The rotor position detectionprocessing circuit 3 is connected to the inputs of the microprocessor 7and the logic circuit 6 via lines 16 and 15, respectively.

Further, in the illustrated embodiment, the motor controller furtherincludes an input device 46, which has a maximum speed setting unit 10for use in setting a target RPM corresponding to various airflow rates.Further the input device 46 includes an airflow rate setting unit 11 forsetting various levels of constant airflow rates. The maximum speedsetting unit 10 and the constant rated airflow setting unit 11 areconnected to a multi-program interface circuit 9 via lines 18 and 19,respectively. The multi-program interface circuit 9 has an outputconnected to the input of the microprocessor 7 via line 17.

The motor controller of the illustrated embodiment further includes aninterface circuit 47, a pulse width modulation (PWM) unit 48, and a DCvariable voltage unit 49. The interface circuit 47 is configured toprocess a PWM signal (generally 80 Hz) for speed setting, which issupplied from the external system or control device through the pulsesignal supply unit 48, and a variable DC voltage (0 to 10V) suppliedfrom the DC variable voltage unit 49 by using a single terminal. Theinterface circuit 47 is connected to the input of the microprocessor 7via line 50.

The microprocessor 7 is configured to process data to control motor soas to operate in a constant airflow rate mode based on the acquired datafrom the sensor circuits, and transmit a PWM signal (for example, 20Khz) for speed control. The output signal is transmitted to the logiccircuit 6 of the electronic control circuit 70 via a line 21.

In one embodiment, the controller has a set of commands for performing aself-testing operation. In the test operation of the ventilation system,when the motor driving power switch 402 turns on, the motor is operatedto rotate the fan from a still state to a preset maximum speed as themicroprocessor 7 outputs a PWM output signal while being automaticallymodulated 0 to 100% according to a self-driving test operation commandsof the microprocessor 7. At this time, from the load current 22 and thespeed signal 16, the microprocessor 7 acquires current data, speed data,and a peak current rate, which may vary according to various differentfan loads and environments, and determines the current-speed relation asshown in FIG. 4.

Now referring to FIG. 15, for example, a variety of fans or blower ofthe fan 1 can be connected to the motor 2 used in a ventilation and airconditioning (HVAC) system. The motor 2 may include an ECM or BLM of asingle-phase, two-phase or three-phase or more. The power switch circuit4 has full bridge FET elements 4AH, 4AL, 4□H, and 4□L, and is connectedto one upper winding of the coil of the motor 2.

Each of gate driving circuit sections 24 and 25 of the gate circuit 5for driving the FET elements of the power switch circuit 4 may include agate drive-dedicated circuit such as IRS2106. The gate circuit 5 isconnected to the power switch circuit 4 and the logic circuit 6 havinglogic circuit units 30 and 31 for processing the speed signal and thePWM signal.

The power switch circuit 4 is connected to the current detection circuit8 having a resistor 26 with a resistance of about 0.1 to 0.5 Ω, aresistor 27, and a capacitor 28 connected to a motor control circuitground. A voltage formed in the resistor 26 is integrated when a currentflows, and the voltage signal is input to an amplifier 29. The voltageis transmitted to the microprocessor 7 via a line 23. In order to inputmotor speed (RPM) information from the rotor position detectionprocessing circuit 3 of the motor 2 employing a sensor or back-EMF of anarmature coil, the signal is transmitted to the input of themicroprocessor 7 via a line 16.

Further, the output of the program input device 46 is connected to atransmission line 39 of a RS485 processor 36. The output signal is tocontrol and monitor a maximum speed setting unit 10 and a constant ratedairflow setting unit 11 enabling a multi-level programming for constantairflow control according to one embodiment. A transmission output R ofthe RS486 processor 36 is connected to a data input RXD of themicroprocessor 7 through a photo coupler 34. A data output 43 of themicroprocessor 7 is connected to a receiving input of the program inputdevice 46 via the photo coupler 33, the RS485 processor 36 and a line40. A data communication control (CTRL) signal 45 of the microprocessor7 is connected to a control terminal of the RS485 processor 36 throughthe photo coupler 35. Accordingly, the program data can be supplied tothe microprocessor 7 smoothly, and grounds 41 and 42 can be electricallyinsulated from an external program input device 46.

Further, an interface circuit (SCI) 47 has a speed signal conversionmicroprocessor 56 built therein. The speed signal conversionmicroprocessor 56 serves to interface a DC variable voltage unit 49 anda pulse width modulator 48 for generating a variable DC voltage of about0 V to about 10 V and a PWM signal, which is used for speed control orsetting, in response to a control signal of an external systemcontroller, to one terminal. Now an embodiment of the speed signalconversion microprocessor 56 is further described.

Referring to FIG. 16, in one embodiment, when a DC variable voltage unit49 is selected by a switch 65, a DC voltage is input to an input PB1 ofthe speed signal conversion microprocessor 56 through an OP amp 58. TheDC voltage passing through a resistor 64 is cut off by a DC filtercapacitor 59. Meanwhile, when a predetermined DC voltage is input to theinput PB1, the speed signal conversion microprocessor 56 is programmedto output a pulse width modulation signal of 80 Hz (an output signalshown in FIG. 15B), which is proportional to a voltage level thereof Theoutput signal PBO of 80 Hz is connected (54) to a base of a transistor53. An output of a photo coupler 52 is connected (55) to a base of atransistor 51. Accordingly, a PWM signal of 80 Hz, which is fullyinsulated electrically, is output through a collector 50 of thetransistor 51.

If a PWM signal of 40 to 120 Hz is connected to the input of the switch65, a signal whose voltage is divided into the resistor 64 and theresistor 63 is input to a base of a transistor 61. An AC component of apulse by switching of the transistor 61 is input to an input PB2 of thespeed signal conversion microprocessor 56 through the two capacitors 59and 60.

The speed signal conversion microprocessor 56 has a program builttherein, for outputting a PWM signal of 80 Hz according to an increaseor decrease of a pulse width on the basis of a rising point a of apulse, a falling point b of the pulse, and a rising point c of 1/f cycleof the pulse, as shown in FIG. 17B, although an input PWM signalfrequency is not constant as in INPUT (40 to 120 Hz) of FIG. 17A.Accordingly, a PWM output of 80 Hz can be always output accuratelyalthough there is a change in an input PWM frequency.

Embodiments of the present invention provide an input method, which iscapable of setting a constant rate point (CRP) and a maximum speed (ortarget RPM). Thus, as shown in A, B, and C of FIG. 8, various levels ofconstant airflows can be set and a constant airflow can be realizedaccurately with a reasonable tolerance and conveniently. According toembodiments of the present invention, although an unknown load isconnected to a motor, the motor can be driven according to aself-driving program and a load current and speed of the motor areautomatically found to calculate a constant airflow control function. Itis thus not necessary to install an additional sensor for detectingstatic pressure inside the duct nor to input constant airflow data.

Further, embodiments of the present invention provide an input methodcapable of arbitrarily setting a constant rated point CRP and a maximumspeed. Accordingly, constant airflows can be set in various ways such as(A), (B), and (C) of FIG. 8, and an accurate constant airflow can be setconveniently. Further, there is an advantage in that a PWM or DCvariable voltage signal for speed control, which is provided from a HAVCsystem controller, can be processed stably and easily. Furthermore,embodiments of the present invention can simplify a constant airflowcontrol device and system, save a time and cost consumed to calculateand set constant airflow program and data necessary for different fansand blowers, and maximize amenity and energy saving effects, which areexpected in HAVC control.

It is to be understood that persons of skill in the appropriate arts maymodify the invention here described while still achieving the favorableresults of this invention. Accordingly, the foregoing disclosure is tobe understood as being a broad, teaching disclosure directed to personsof skill in the appropriate arts, and not as limiting upon theinvention.

1. A method of operating an electric motor in a ventilation system, themethod comprising: providing a blower comprising a motor and a fancoupled to the motor, the blower being configured to generate an airflowin a ventilation duct; monitoring a rotational speed of the motor;monitoring an electric current applied to a motor; comparing theelectric current against a reference value; and controlling the motor'soperation such that the rotational speed is substantially maintainedwithin proximity of a target rotational speed when the electric currentis smaller than the reference value, and controlling the motor'soperation such that the rotational speed stays generally inverselyproportional to the electric current when the electric current isgreater than the reference value.
 2. The method of claim 1, whereincontrolling the motor's operation generates a substantially constantairflow rate while a static pressure within the duct significantlychanges.
 3. The method of claim 2, wherein the system does not comprisean airflow rate sensor for detecting an airflow rate generated by theblower, wherein controlling the motor's operation does not use an inputof an airflow rate generated by the blower.
 4. The method of claim 3,wherein the system does not comprise a static pressure sensor fordetecting the static pressure within the duct, wherein controlling themotor's operation does not use an input of a static pressure within theduct.
 5. The method of claim 1, wherein controlling the motor'soperation comprises adjusting a turn-on period of the motor so as toattempt to make the rotational speed reach the target rotational speed.6. The method of claim 1, further comprising receiving a user's input ofa desired rotational speed, which becomes the target rotational speed.7. The method of claim 1, wherein the target rotational speed is afractional value of a rated rotational speed of the motor.
 8. The methodof claim 1, further comprising: receiving a user input of a desiredlevel of the rotational speed, wherein the user input comprises aselection among a plurality of predetermined levels; and retrieving,from a memory, the target rotational speed associated with the user'sselection.
 9. The method of claim 1, further comprising: receiving auser input of a desired level of the rotational speed, wherein the userinputs the desired level represented in a number; and computing thetarget rotational speed using the number and a preprogrammed formula.10. The method of claim 9, wherein the target rotational speed iscomputed using the number and a rated rotational speed of the motor. 11.The method of claim 1, wherein controlling the motor's operation suchthat the rotational speed stays generally inversely proportional to theelectric current comprising maintaining a product of the electriccurrent and the rotational speed within proximity of a target productvalue.
 12. The method of claim 11, wherein the target product value iscomputed using a rated electric current and a rated rotational speed ofthe motor.
 13. A method of operating an electric motor in a ventilationsystem, the method comprising: providing a blower comprising a motor anda fan coupled to the motor, the blower being configured to generate anairflow in a ventilation duct; detecting an electric current applied tothe motor; detecting a rotational speed of the motor; and controllingthe motor's operation so as to generate the airflow with a substantiallyconstant airflow even if a static pressure within the duct substantiallychanges, wherein controlling the motor's operation does not use an inputof an airflow rate generated by the blower, controlling the motor'soperation such that the rotational speed is substantially maintainedwithin proximity of a target rotational speed when the electric currentis smaller than the reference value, and controlling the motor'soperation such that the rotational speed stays generally inverselyproportional to the electric current when the electric current isgreater than the reference value.
 14. The method of claim 13, whereinthe system does not comprise an airflow rate sensor for detectingchanges of the airflow rate.
 15. The method of claim 13, wherein thesystem does not comprise a static pressure sensor for detecting a staticpressure within the duct, and wherein controlling the motor's operationdoes not use an input of a static pressure within the duct.
 16. Themethod of claim 13, wherein controlling the motor's operation such thatthe rotational speed is substantially maintained within proximity of atarget rotational speed comprises a feedback control of the rotationalspeed so as to make the rotational speed reach the target rotationalspeed.
 17. The method of claim 13, wherein controlling the motor'soperation such that the rotational speed stays generally inverselyproportional to the electric current comprises a feedback control of aproduct of the electric current and the rotational speed so as to makethe product reach a target product value.